Creating a script

Offering income for a web developer. It is required to create a script for the site of the trading platform, where the cheapest are exhibited among the same goods first of all - even if they are one penny cheaper. The purpose of the script I need is to automatically change the prices of my product at the cheapest price of the site, but up to the limit, i.e., the price of my product is not the same. So that the price does not fall below any limits. If there is a price below the frame, the price should return to the initial set. With auto purchase, the situation is similar - I buy the product first, if my request is higher than all others, but also need to reach certain limits.